The main site http://www.xsane.org has vanished. The sources are available at the project page of the sane-project at GitLab.
The GL_* variables are used a bit differently to retrieve the tarball from a Gitlab subproject and to avoid slashes in the DISTNAME. Please see the comments in the diff for further details.
Also while I'm here:
- Add "gnome" to USES as using USE_GNOME alone is deprecated.
PR: 237875
Reported by: Nick Godson